This invention relates to a multiple control valve for controlling the operation of, for example, a hydraulic power shovel of a civil construction machine or vehicle.
A hydraulic power shovel generally comprises a lower travelling portion and an upper rotating portion including an operator's cab, a boom, an arm, and a bucket, and a multiple control valve of the power shovel comprises a plurality of parallelly arranged plungers which hydraulically control respective portions of the power shovel. With the multiple control valve of this type, which requires at least two plungers, i.e. direction change-over valves, when the plungers for rotating the rotary portion and operating the arm of the power shovel are changed over to thereby simultaneously operate the rotary portion and the arm, and in this case, when a load applied to the arm is small, a sufficient pumping pressure cannot be obtained, and therefore, a pressure for rotating the rotary portion cannot be maintained at a sufficient value, and sometimes, there arises a case where the rotating operation cannot be performed. In a prior art control valve, in order to obviate this defect, a multiple control valve is provided with a valve having a throttling function between parallel circuits connecting plungers for rotating the rotary portion and the arm of the shovel so as to maintain a desired rotating pressure in a case when a light load is applied on the arm.
However, the provision of such valve between the parallel circuits requires a space in the multiple control valve which unwillingly enlarge the valve body thereof, and moreover, in a case where only the plunger for operating the arm is operated, since the fluid in the plunger for rotation is fed into the arm plunger through the throttle valve, unnecessary pressure loss would be caused.